Radio broadcasting and receiving



Dec. 26, 1933. E. H. ARMSTRONG 1,941,067 I RADIO BROADCASTING ANDREbEIVING Filed Oct. 20, 1932 HNNUU/VCEMENT mama/0y /Z HMPur/aeflMPUF/EE STUD/0 m/ceapya a I INVENTOR Edwin H Army/m4 BY MWM.

A TTORNEYS Patented Dec. 26, 1933 UNITED STATES PATENT OFFICE 3 Claim.

This invention relates to a method of solving a problem in broadcastreception. This problem is the separation of entertainment programs fromundesired advertising talks, by the automatic operation of the receivingapparatus so that the listener is spared the effort of manuallyoperating his set.

The problem is solved by providing at the broadcast transmitter aninaudible modulating frequency which is automatically put on thetransmitter whenever the advertising talk is being made and providing atthe receiver a selective receiving means to receive this steady tone andto cause it to operate a relay which cuts off the loud speaker of thereceiver. When the advertising talk is finished the auxiliary modulatingfrequency at the transmitter is cut off, the relay at the receiverreconnects the loud speaker and the set is in condition to receive thedesired v part of the program.

In the drawing forming part of this specification,

Figure 1 illustrates the general arrangement of the transmitting system;and

Figure 2 illustrates thegeneral arrangement of the receiving system forcarrying out this invention.

Referring now to Figure 1, 12 represents the announcement microphone andits associated amplifying system and 3-4 represents the studiomicrophone and amplifier for picking up the musical part of the program.5-6 is a switch for throwing over from one microphone to the other and 7is a simultaneously operated switch for throwing on to the modulatinginput to the radio transmitter 11 a sub-audible modulating current fromthe source 89-10. A frequency of the order of 20 cycles may be used.This frequency is chosen so that it will be inaudible and will nottherefore affect the reception on ordinary receivers not equipped withthe automatic cut out.

Referring now to Figure 2, 14 represents the output transformer of anordinary broadcast receiver. 151617 is a filter designed to pass thesub-audible frequency but to cut off the frequencies which are normallytransmitted in the musical program. 18 is a potentiometer to adjust theinput to the amplifier 19-23. The last tube 23 of the amplifier isbiased to cut off by the battery 22. The plate circuit of the tube 23contains a relay 25, the contact of which is normally held closed by thespring 26, thereby keeping the loud speaker circuit normally closed.

The operation of the system is as follows:

When the switch 5-6-7 at the transmitter is in position A, thetransmitter operates in the ordmary way. The broadcast receiver alsooperates in the ordinary way. The filter 151617 cuts off the frequenciesused in the transmission of music so that the amplifier and relayremains inoperative. When, however, the switch is thrown to theannouncement microphone in position B, a constant inaudible modulationis immediately impressed on the transmitter. This is received by thebroadcast receiver, passes through the filter 15-161'7- and is amplifiedup to a point where it actuates the relay 25 cutting off the loudspeaker 27. This condition is maintained until the studio microphone isconnected in place of the announcement microphone, when upon removal ofthe subaudible frequency the relay arm isreleased and again completesthe relay circuit.

Where the listener desires to receive the advertising part of theprogram he may do so by closing the switch 28.

Instead of a sub-audible auxiliary frequency, a super-audible frequencywith suitable modification of the filtering means at the receiver 30 maybe used.

To compensate for different adjustments of p the receiver to producevarying degrees of loudness and to insure the operation of the automaticcut off device on various signal strengths, the bias of the amplifiertubes 20, 23 may be arranged to be controlled by the strength of thecarrier supplied to the detector tube in any of the well-known methodsof accomplishing automatic volume control. 99

Instead of the filter 15, 16, 17 a tuned circuit or a plurality of themtuned to the sub-audible or superaudible frequency may, of course, beused.

I have described what I believe to be the best embodiments of myinvention. I do not wish, however, to be confined to the embodimentsshown, but what I desire to cover by Letters Patent is set forth in theappended claims.

I claim: 100

l. The method of enabling a listener to separate entertainment programsfrom undesired advertising talks in radio broadcasting to a multiplicityof receiving stations, which consists in transmitting with theadvertising talk an inaudible frequency, selecting said inaudiblefrequency at the receiver, and selectively causing said inaudiblefrequency at the receiver to render the loud speaker thereof inoperativeas long as the inaudible frequency is being received.

3. A receiver for use in the system of claim 2, said receiver comprisinga loud speaker, means responsive to current of inaudible frequency torender said loud speaker inoperative, and manually operable means torender said first mentioned means ineffective to control the loudspeaker.

EDWIN H. ARMSTRONG.

